It is economically desirable to reclaim scrap metal, such as turnings, chips, shearings, punchings, borings, gates, risers, and the like, so that the reclaimed scrap can be used as melting stock or used in chemical processes, or briquetted for use as a charge material in foundry practice.
The use of metal scrap has certain drawbacks in that the scrap is small dimensionally and is normally coated with oil. If the oil coated scrap is used as melting stock, the oil will be combusted during the melting process and the resulting smoke is difficult to control in the foundry. Furthermore, the oil coating can cause slag problems in the melt. If the oil coated metal scrap is briquetted, any residual oil can have an adverse effect on the bond between the scrap particles in the briquette.
Because of this, it is common practice to remove the oil and other organic contaminants from the metal scrap by passing the scrap through an inclined, heated retort or drum. The contaminated scrap is introduced into the upper end of the retort, and as the scrap is conveyed downwardly to the lower end the combustible materials are heated and vaporized.
In one method, sufficient heat is supplied to merely vaporize the moisture, oil or other organic contaminants, and the vapors are then delivered to an afterburner where the vapors are burned.
In another commonly used method, controlled, partial combustion of the oil is effected in the retort in which a sefl-supporting flame is maintained in at least a portion of the length of the retort. With this system, it is necessary to exercise close temperature control within the retort in order to prevent oxidation, fusing or melting of the metal scrap. In the past, attempts have been made to provide temperature control for the metal scrap by introducing water into the retort when the temperature exceeds a pre-determined maximum, as suggested by U.S. Pat. No. 3,767,179. However, it is difficult to accurately control the amount of water added to maintain the scrap at a precise temperature.